U.S. patent application number 12/877403 was filed with the patent office on 2011-04-21 for image display apparatus.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Hiroshi Hasegawa, Ryoki WATANABE.
Application Number | 20110090465 12/877403 |
Document ID | / |
Family ID | 43879057 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110090465 |
Kind Code |
A1 |
WATANABE; Ryoki ; et
al. |
April 21, 2011 |
IMAGE DISPLAY APPARATUS
Abstract
An image display apparatus includes: a light source system that
emits light having a first wavelength and a second wavelength
switched with time; a light modulator that modulates the light
having the first wavelength and the second wavelength emitted from
the light source system; an optical path adjustment system that
shifts the optical paths of the light having the first wavelength
and the second wavelength modulated by the light modulator from
each other; and the optical path adjustment system, wherein the
optical path adjustment system includes a wavelength selecting
surface that reflects the light having the first wavelength and
transmits the light having the second wavelength, and mirror system
disposed in such a way that the optical paths of the light having
the first wavelength and the second wavelength having traveled via
the wavelength selecting surface are shifted from each other.
Inventors: |
WATANABE; Ryoki;
(Shiojiri-shi, JP) ; Hasegawa; Hiroshi;
(Chino-shi, JP) |
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
43879057 |
Appl. No.: |
12/877403 |
Filed: |
September 8, 2010 |
Current U.S.
Class: |
353/31 |
Current CPC
Class: |
G03B 21/28 20130101;
H04N 9/3188 20130101; H04N 9/3111 20130101 |
Class at
Publication: |
353/31 |
International
Class: |
G03B 21/28 20060101
G03B021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2009 |
JP |
2009-242512 |
Claims
1. An image display apparatus comprising: a light source system
that emits light having a first wavelength and light having a
second wavelength switched with time; a light modulator that
modulates the light having the first wavelength and the light
having the second wavelength emitted from the light source system;
an optical path adjustment system that shifts the optical paths of
the light having the first wavelength and the light having the
second wavelength modulated by the light modulator from each other;
and a projection system that projects the light having traveled via
the optical path adjustment system, wherein the optical path
adjustment system includes: a wavelength selecting surface that
reflects the light having the first wavelength and transmits the
light having the second wavelength; and a mirror system disposed in
such a way that the optical paths of the light having the first
wavelength and the light having the second wavelength having
traveled via the wavelength selecting surface are shifted from each
other but the traveling directions thereof are the same.
2. The image display apparatus according to claim 1, wherein the
optical path adjustment system produces the amount of shift by
which the optical path of the light having the first wavelength and
the optical path of the light having the second wavelength are
shifted from each other in such a way that a pixel formed by the
light having the first wavelength overlaps with a plurality of
pixels formed by the light having the second wavelength in an
imaging plane where the light projected through the projection
system is focused.
3. The image display apparatus according to claim 1, wherein the
mirror system is formed of a reflection surface disposed
substantially in parallel to the wavelength selecting surface.
4. The image display apparatus according to claim 3, wherein the
wavelength selecting surface is formed on the same optical element
on which the reflection surface is formed.
5. The image display apparatus according to claim 1, wherein the
light source system includes a first solid-state light source, that
emits light having the first wavelength and a second solid-state
light source that emits light having the second wavelength, and the
first and second solid-state light sources are driven in such a way
that the period during which the first solid-state light source is
turned on is shifted from the period during which the second
solid-state light source is turned on.
6. The image display apparatus according to claim 5, further
comprising a controller that controls the light source system and
the light modulator, wherein the controller supplies a first
modulation signal corresponding to an image to be displayed by
using the light having the first wavelength and a second modulation
signal corresponding to an image to be displayed by using the light
having the second wavelength to the light modulator switched with
time to turn on the first solid-state light source in
synchronization with the first modulation signal and turn on the
second solid-state light source in synchronization with the second
modulation signal.
7. The image display apparatus according to claim 5, wherein at
least one of the first and second solid-state light sources is
formed of a light emitting diode.
8. The image display apparatus according to claim 5, wherein at
least one of the first and second solid-state light sources is
formed of a laser diode.
9. The image display apparatus according to claim 1, further
comprising: a second light source system that emits light having a
third wavelength longer than the first and second wavelengths; a
third light source system that emits light having a fourth
wavelength shorter than the first and second wavelengths; a second
light modulator that modulates the light emitted from the second
light source system; a third light modulator that modulates the
light emitted from the third light source system; and a light
combining element that combines the light modulated by the light
modulator, the light modulated by the second light modulator, and
the light modulated by the third light modulator, wherein the
wavelength selecting surface reflects one of light having a
wavelength longer than a predetermined wavelength between the first
and second wavelengths and light having a wavelength shorter than
the predetermined wavelength and transmits the other light, the
optical paths of the light fluxes that exit out of the light
combining element are configured in such a way that one of the
optical path of the light having the third wavelength and the
optical path of the light having the fourth wavelength
substantially coincides with the optical path of the light having
the first wavelength, and that the optical path of the light having
the third wavelength is shifted from the optical path of the light
having the fourth wavelength, and the amount of shift by which the
optical path of the light having the third wavelength that exits
out of the light combining element and the optical path of the
light having the fourth wavelength that exits out of the light
combining element are shifted from each other is set in such a way
that the optical path of the light of the third wavelength having
traveled via the optical path adjustment system substantially
coincides with the optical path of the light of the fourth
wavelength having traveled via the optical path adjustment system.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to an image display
apparatus.
[0003] 2. Related Art
[0004] It is hoped that projectors and other image display
apparatus can display an image at higher resolution. When an image
formed by using a light modulator, such as liquid crystal light
valve, is displayed, the number of pixels of the image displayed on
a screen or any other surface is typically equal to the number of
pixels of the light modulator. Increasing the resolution of the
light modulator increases the resolution of the displayed image but
results in significant increase in manufacturing cost.
[0005] To produce a high-resolution displayed image without
increasing the resolution of the light modulator, it is conceivable
to increase the number of light modulators. Forming images by using
a plurality of light modulators and projecting the thus formed
images in such a way that the position of each pixel of one image
is shifted from those of the other images allow the total number of
pixels on the screen to be increased. In this method, however,
since the number of light modulators is increased, the cost
increases accordingly. As a technique for solving the inconvenience
described above, instead of increasing the number of light
modulating devices to form a plurality of images, a method for
forming a plurality of images in a time division manner by using a
single light modulator has been proposed (JP-A-11-298829 and
JP-A-2005-91519, for example).
[0006] In the image display apparatus described in JP-A-11-298829
and JP-A-2005-91519, image light formed by a light modulator in a
time division manner is projected through a flat-plate prism. The
flat-plate prism is inclined to the direction in which the image
light is incident. The image light incident on the flat-plate prism
exits therethrough with the optical path of the image light shifted
in parallel. The amount of shift of the optical path before the
light is incident on the flat-plate prism from the optical path
after the light is incident on the flat-plate prism is controlled
in synchronization with image formation. As a method for changing
the amount of shift with time, JP-A-11-298829 describes the
following first to third methods, and JP-A-2005-91519 describes a
fourth method.
[0007] In a first method, the inclination angle of a flat-plate
prism is changed with time. In a second method, a flat-plate prism
formed of portions that produce different amounts of refraction is
rotated to change with time the amount of refraction produced in
the portion through which image light passes. In a third method, a
flat-plate prism is made of a nonlinear optical crystal the
refractive index of which can be variably controlled by applying an
electric field, and the applied electric field is changed with
time. In a fourth method, a light blocker is provided between the
portions that produce different amounts of refraction in the second
method.
[0008] The techniques described in JP-A-11-298829 and
JP-A-2005-91519 have the following problems:
[0009] In the first, second, and fourth methods, the flat-plate
prism could vibrate when spatially displaced. If the flat-plate
prism vibrates, the amount of shift of the optical path changes
unexpectedly, which makes it difficult to control the amount of
shift with high precision, resulting in a decrease in the quality
of a displayed image. An attempt to synchronize the displacement of
the flat-plate prism with image formation in a spatial light
modulator with high precision makes a mechanism for spatially
moving the flat-plate prism complicated. Further, the vibration of
the flat-plate prism could produce noise and shorten the lifetime
thereof.
[0010] In the first method, since images are displayed even while
the pixels are shifted, the image could be blurred. In the second
method, since the pixels in the vicinity of the boundary between
the portions that produce different amounts of refraction are
separated, and the pixel shift timing on one end side of a
displayed image differs from the pixel shift timing on the other
end side of the displayed image, for example, the quality of the
displayed image could decrease. Although employing the fourth
method can prevent the pixels from being separated, the problem of
the difference in the pixel shift timing in a displayed image is
still unsolved.
[0011] In the third method, the size of the nonlinear optical
crystal needs to be greater than or equal to the spot size of
incident image light. Applying an electric field strong enough to
ensure the amount of shift necessary to provide a sense of high
resolution to the thus sized nonlinear optical crystal requires a
voltage higher than those for driving a light modulator and other
components, resulting in an increase in voltage required to drive
the entire image display apparatus.
[0012] In the third method, using the Kerr effect disadvantageously
increases the cost of the nonlinear optical crystal, resulting in
loss of superiority over a method of increasing the number of light
modulators. On the other hand, using the Pockels effect results in
a decrease in light usage efficiency because the visible light
transmittance of the nonlinear optical crystal decreases, necessity
of controlling the state of the nonlinear optical crystal, and
other inconveniences. As described above, it is not realistic to
variably control the optical path of image light by using a
nonlinear optical crystal.
SUMMARY
[0013] An advantage of some aspects of the invention is to provide
an image display apparatus capable of displaying a high-quality
image.
[0014] An image display apparatus of an aspect of the invention
includes a light source system that emits light having a first
wavelength and light having a second wavelength switched with time,
a light modulator that modulates the light having the first
wavelength and the light having the second wavelength emitted from
the light source system, an optical path adjustment system that
shifts the optical paths of the light having the first wavelength
and the light having the second wavelength modulated by the light
modulator from each other, and a projection system that projects
the light having traveled via the optical path adjustment system.
The optical path adjustment system includes a wavelength selecting
surface that reflects the light having the first wavelength and
transmits the light having the second wavelength and a mirror
system disposed in such a way that the optical paths of the light
having the first wavelength and the light having the second
wavelength having traveled via the wavelength selecting surface are
shifted from each other but the traveling directions thereof are
the same.
[0015] The light emitted from the light source system is modulated
by the light modulator. The light modulated by the light modulator
travels via the optical path adjustment system, is projected
through the projection system, and is displayed as an image. Since
the light source system emits light having a first wavelength and
light having a second wavelength switched with time, the modulated
light having the first wavelength and the modulated light having
the second wavelength are incident on the wavelength selecting
surface switched with time. Since the optical paths of the light
having the first wavelength and the light having the second
wavelength are shifted from each other when they travel via the
wavelength selecting surface and the mirror system, an image formed
by the projected light having the first wavelength and an image
formed by the projected light having the second wavelength are
displayed in positions shifted from each other.
[0016] According to the image display apparatus of the aspect of
the invention, an image corresponding to the first wavelength and
an image corresponding to the second wavelength can be displayed
with their positions temporally and spatially shifted from each
other without dynamic control of the optical path adjustment system
itself. Unlike a case where a flat-plate prism or any other similar
component is spatially displaced to shift the optical paths from
each other, the optical path adjustment system will not vibrate and
any adverse effect due to vibration will not occur. Further, unlike
a case where the refractive index of a nonlinear optical crystal is
variably controlled in an electrical manner, the voltage for
driving the image display apparatus will not increase. Moreover,
since the entire light flux having the first wavelength or the
entire light flux having the second wavelength can be collectively
shifted, the pixels can be shifted in a displayed image at the same
timing. As described above, the invention provides an image display
apparatus capable of displaying a high-quality image.
[0017] The image display apparatus according to the aspect of the
invention can be implemented in the following representative
forms.
[0018] The optical path adjustment system may produce the amount of
shift by which the optical path of the light having the first
wavelength and the optical path of the light having the second
wavelength are shifted from each other in such a way that a pixel
formed by the light having the first wavelength overlaps with a
plurality of pixels formed by the light having the second
wavelength in an imaging plane where the light projected through
the projection system is focused.
[0019] In this way, pixels formed by the light having the first
wavelength can fill the gaps between pixels formed by the light
having the second wavelength, whereby the resolution of a displayed
image can be effectively increased.
[0020] The mirror system may be formed of a reflection surface
disposed substantially in parallel to the wavelength selecting
surface.
[0021] In this way, the optical path of the light of the second
wavelength reflected on the reflection surface is substantially
parallel to the optical path of the light of the first wavelength
reflected on the wavelength selecting surface. The amount of shift
by which the optical paths are shifted from each other in the
optical path adjustment system can therefore be determined by the
distance between the wavelength selecting surface and the
reflection surface and the angle of incidence of the light incident
on the wavelength selecting surface. The optical path adjustment
system having a simple configuration can still set the amount of
shift by which the optical paths are shifted from each other with
high precision.
[0022] The wavelength selecting surface may be formed on the same
optical element on which the reflection surface is formed.
[0023] As compared with a case where the wavelength selecting
surface and the reflection surface are formed on separate elements,
the relative positional relationship between the wavelength
selecting surface and the reflection surface can be set with high
precision, whereby change in the relative positional relationship
between the wavelength selecting surface and the reflection surface
over time can be significantly reduced. Further, the number of
interfaces between the wavelength selecting surface and the
reflection surface can be reduced, whereby light loss at the
interfaces can be reduced.
[0024] The light source system may include a first solid-state
light source that emits light having the first wavelength and a
second solid-state light source that emits light having the second
wavelength, and the first and second solid-state light sources may
be driven in such a way that the period during which the first
solid-state light source is turned on is shifted from the period
during which the second solid-state light source is turned on.
[0025] In this way, the period during which the first solid-state
light source is turned on can be shifted from the period during
which the second solid-state light source is turned on through
electrical control. As a result, the light emitted from the light
source system can be readily switched with time between the light
having the first wavelength and the light having the second
wavelength. Further, the period during which the first solid-state
light source is turned on and the period during which the second
solid-state light source is turned on can be controlled with high
precision.
[0026] The image display apparatus may further include a controller
that controls the light source system and the light modulator, and
the controller may supply a first modulation signal corresponding
to an image to be displayed by using the light having the first
wavelength and a second modulation signal corresponding to an image
to be displayed by using the light having the second wavelength to
the light modulator switched with time to turn on the first
solid-state light source in synchronization with the first
modulation signal and turn on the second solid-state light source
in synchronization with the second modulation signal.
[0027] In this way, the timing at which the light having the first
wavelength is incident on the light modulator can be precisely
synchronized with the timing at which the light having the first
wavelength is modulated in accordance with an image to be displayed
by using the light having the first wavelength. Further, the timing
at which the light having the second wavelength is incident on the
light modulator can be precisely synchronized with the timing at
which the light having the second wavelength is modulated.
[0028] At least one of the first and second solid-state light
sources may be formed of a light emitting diode.
[0029] In this way, the lifetime of the light source system and
hence the lifetime of the image display apparatus can be prolonged.
As compared with a case where a laser diode is used as the
solid-state light source, light within a desired wavelength band is
readily obtained, and the configuration of the light source system
can be simplified.
[0030] At least one of the first and second solid-state light
sources may be formed of a laser diode.
[0031] In general, since the spectral bandwidth of laser light is
significantly narrower than the spectral bandwidth of the light
emitted from a light emitting diode (LED) or any other similar
device, the light having the first wavelength and the light having
the second wavelength can be readily separated with high precision
at the wavelength selecting surface.
[0032] The image display apparatus may further include a second
light source system that emits light having a third wavelength
longer than the first and second wavelengths, a third light source
system that emits light having a fourth wavelength shorter than the
first and second wavelengths, a second light modulator that
modulates the light emitted from the second light source system, a
third light modulator that modulates the light emitted from the
third light source system, and a light combining element that
combines the light modulated by the light modulator, the light
modulated by the second light modulator, and the light modulated by
the third light modulator. The wavelength selecting surface may
reflect one of light having a wavelength longer than a
predetermined wavelength between the first and second wavelengths
and light having a wavelength shorter than the predetermined
wavelength and transmit the other light. The optical paths of the
light fluxes that exit out of the light combining element may be
configured in such a way that one of the optical path of the light
having the third wavelength and the optical path of the light
having the fourth wavelength substantially coincides with the
optical path of the light having the first wavelength, and that the
optical path of the light having the third wavelength is shifted
from the optical path of the light having the fourth wavelength.
The amount of shift by which the optical path of the light having
the third wavelength that exits out of the light combining element
and the optical path of the light having the fourth wavelength that
exits out of the light combining element are shifted from each
other is set in such a way that the optical path of the light of
the third wavelength having traveled via the optical path
adjustment system substantially coincides with the optical path of
the light of the fourth wavelength having traveled via the optical
path adjustment system.
[0033] In this way, the light emitted from the light source system,
the light emitted from the second light source system, and the
light emitted from the third light source system are modulated by
the light modulator, the second light modulator, and the third
light modulator, respectively, and then combined in the light
combining element. In the combined light, the relative relationship
between the optical path of the light having the third wavelength
and the optical path of the light having the fourth wavelength
changes before and after they travel via the optical path
adjustment system. The optical path of the light having the third
wavelength and the optical path of the light having the fourth
wavelength, which are shifted from each other before they are
incident on the optical path adjustment system, substantially
coincide with each other after they travel via the optical path
adjustment system. As a result, the position of each pixel formed
by the light having the third wavelength and the position of each
pixel formed by the light having the fourth wavelength
substantially coincide with the position of each pixel formed by
one of the light having the first wavelength and the light having
the second wavelength.
[0034] As described above, since the light fluxes having the first
to fourth wavelengths can form and display an image having a large
number of hues, the resultant image display apparatus can display a
high-quality image. Further, the position where each pixel formed
by the following three light fluxes, one of the light having the
first wavelength and the light having the second wavelength, the
light having the third wavelength, and the light having the fourth
wavelength, is displayed is shifted from the position where each
pixel formed by the other one of the light having the first
wavelength and the light having the second wavelength is displayed,
and the displayed image as a whole forms a high-resolution image.
As described above, since the single optical path adjustment system
can adjust the optical paths of the light fluxes having the first
to fourth wavelengths, the configuration of the image display
apparatus can be simplified and the resolution of an image can be
effectively increased at the same time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0036] FIGS. 1A and 1B are schematic views showing the
configuration of an image display apparatus of a first
embodiment.
[0037] FIGS. 2A and 2B are conceptual diagrams of an image display
method based on pixel shifting.
[0038] FIG. 3 is a schematic view showing the configurations of a
light source system, a light modulator, and a controller.
[0039] FIG. 4 is a chart showing an example of the timing at which
the light source system and the light modulator operate.
[0040] FIG. 5 is a chart showing an example of the operation timing
different from that shown in FIG. 4.
[0041] FIG. 6 is a conceptual diagram showing an example of a
method for generating a modulation signal.
[0042] FIG. 7 shows enlarged pixels to describe the method for
generating a modulation signal.
[0043] FIG. 8 is a conceptual diagram showing an example of a
method for generating a modulation signal different from the method
shown in FIGS. 6 and 7.
[0044] FIG. 9A is a perspective view showing the configuration of
an optical path adjustment system; FIG. 9B is a projection onto an
XZ plane showing the light traveling via the optical path
adjustment system; and FIG. 9C is a projection onto an XY plane
showing the light traveling via the optical path adjustment
system.
[0045] FIG. 10 shows graphs illustrating the characteristics of a
wavelength selecting surface versus first and second
wavelengths.
[0046] FIGS. 11A and 11B are schematic views showing the
configurations of first and second variations.
[0047] FIGS. 12A to 12C are schematic views showing the
configurations of third to fifth variations.
[0048] FIG. 13 is a schematic view showing the configuration of a
sixth variation.
[0049] FIG. 14 is a schematic view showing the configuration of an
image display apparatus of a second embodiment.
[0050] FIG. 15 is a schematic view showing the shift of an optical
path in the second embodiment.
[0051] FIG. 16A is a timing chart showing image display timing for
each hue, and FIG. 16B is a conceptual diagram of an entire
displayed image.
[0052] FIG. 17 is a schematic view showing the configuration of an
image display apparatus of a third embodiment.
[0053] FIG. 18 is a schematic view showing the shift of an optical
path in the third embodiment.
[0054] FIG. 19 shows graphs illustrating the characteristics of a
wavelength selecting surface versus first to fourth
wavelengths.
[0055] FIG. 20A is a timing chart showing image display timing for
each hue, and FIG. 20B is a conceptual diagram of an entire
displayed image.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0056] Embodiments of the invention will be described below with
reference to the drawings. In the drawings used in the description,
the dimensions and scales of structures in the drawings sometimes
differ from actual dimensions and scales of the structures in order
that characteristic portions are readily understood. Optical paths
are sometimes not drawn as they are but are represented only by
their central axes. Similar components in the embodiments have the
same reference characters, and no detailed description thereof will
be made in some cases.
First Embodiment
[0057] FIGS. 1A and 1B are schematic views showing the
configuration of a projector (image display apparatus) 1 of a first
embodiment. FIG. 1A shows a state in which an image formed by light
having a first wavelength is displayed. FIG. 1B shows a state in
which an image formed by light having a second wavelength is
displayed. FIG. 1B also shows the light having the first wavelength
to compare it with the light having the second wavelength. FIG. 2A
is a conceptual diagram showing an image display method based on
pixel shifting. FIG. 2B is an enlarged plan view showing pixels of
an image displayed by using the pixel shifting.
[0058] As shown in FIGS. 1A and 1B, the projector 1 includes a
light source system 2, a light modulator 3, a controller 4, an
optical path adjustment system 5, and a projection system 6. The
projector 1 generally operates as follows:
[0059] The light source system 2 emits light L1 having a first
wavelength and light L2 having a second wavelength different from
the first wavelength switched with time. The light L1 and L2
emitted from the light source system 2 is incident on the light
modulator 3 and modulated thereby. The controller 4 controls the
timing at which the light L1 and the light L2 are emitted from the
light source system 2 and supplies a first modulation signal for
modulating the light L1 and a second modulation signal for
modulating the light L2 switched with time to the light modulator 3
in synchronization with the timing described above.
[0060] The light L1 and the light L2 modulated by the light
modulator 3 are incident on the optical path adjustment system 5 in
a time sequential manner. Looking at the optical paths of the light
L1 and the light L2 before they are incident on the optical path
adjustment system 5, one can see that the optical path A1 of the
light L1 having the first wavelength substantially coincides with
the optical path A2 of the light L2 having the second wavelength.
The optical path adjustment system 5 includes a wavelength
selecting surface 51 characterized by reflecting the light L1 and
transmitting the light L2 and a reflection surface (mirror system)
52 that reflects the light L2 having the second wavelength having
passed through the wavelength selecting surface 51. The light L1 is
reflected on the wavelength selecting surface 51 and incident on
the projection system 6. The light L2 passes through the wavelength
selecting surface 51, is reflected on the reflection surface 52,
passes through the wavelength selecting surface 51 again, and
enters on the projection system 6.
[0061] As shown in FIG. 1B, the optical path A2 of the light L2
having traveled via the optical path adjustment system 5 is shifted
from the optical path A1 of the light L1 having traveled via the
optical path adjustment system 5. Looking at the optical paths of
the light L1 and the light L2 having exited out of the optical path
adjustment system 5, one can see that the optical path A2 of the
light L2 having the second wavelength is substantially parallel to
the optical path A1 of the light L1 having the first wavelength.
Further, the optical path A1 of the light L1 having the first
wavelength and the optical path A2 of the light L2 having the
second wavelength are shifted from each other in a direction
substantially perpendicular to the direction in which the light L1
having the first wavelength and the light L2 having the second
wavelength travel.
[0062] The light L1 and the light L2 having traveled via the
optical path adjustment system 5 enters the projection system 6 in
a time sequential manner and are projected on a projection surface
(a surface on which an image is focused) S, such as a screen.
[0063] As shown in FIG. 2A, a first image B1 formed by the light L1
projected on the projection surface S is displayed and a second
image B2 formed by the light L2 projected on the projection surface
S is displayed. Since the optical path of the light L1 having
exited out of the projection system 6 is shifted from the optical
path of the light L2 having exited out of the projection system 6,
the position of each pixel P1 that forms the first image B1 is
shifted from the position of each pixel P2 that forms the second
image B2 as shown in FIG. 2B. The images B1 and B2 are displayed
while being switched with time at a speed high enough not to let a
viewer be aware of the switching. The viewer observes the images B1
and 82 superimposed with the positions of the pixels P1 and P2
shifted from each other, whereby an effectively higher resolution
image is displayed. The components of the projector 1 will be
described below in detail.
[0064] FIG. 3 is a schematic view showing the configurations of the
light source system 2, the light modulator 3, and the controller 4,
and FIG. 4 is a timing chart showing an example of the timing at
which the light source system 2 and the light modulator 3
operate.
[0065] As shown in FIG. 3, the light source system 2 includes a
light emitting panel 20 and a driver 21. The light emitting panel
20 has a plurality of first solid-state light sources 22 and a
plurality of second solid-state light sources 23 arranged therein
in a two-dimensional manner. The first solid-state light sources
and the second solid-state light sources 23 are alternately
arranged in two arrangement directions.
[0066] Each of the solid-state light sources 22 and 23 is formed of
a light emitting diode (LED), a laser diode (LD), or any other
suitable solid-state light source. In the present embodiment, each
of the solid-state light sources 22 and 23 is formed of an LED.
Each of the first solid-state light sources 22 emits the light L1,
the intensity peak of which occurs at the first wavelength, and
each of the second solid-state light sources 23 emits the light L2,
the intensity peak of which occurs at the second wavelength
different from the first wavelength. When each of the solid-state
light sources 22 and 23 is formed of an LED, green light can be
directly produced more easily than by using an LD. Further, the
light source system 2 formed of LEDs consumes less electric power
and lasts longer than in a case where a lamp-based light source is
used.
[0067] It is herein assumed that the second wavelength is selected
from a wavelength band that belongs to a hue (green, for example)
that is substantially the same as a hue to which the first
wavelength belongs and that the second wavelength is shorter than
the first wavelength. The difference between the first and second
wavelengths is set at a value that allows the light L1 and the
light L2 can be separated at the wavelength selecting surface or a
value greater than the thus set value. The difference between the
first and second wavelengths, for example, ranges from
approximately 10 to 100 nm.
[0068] The driver 21 turns on and off the plurality of first
solid-state light sources 22 together. The driver 21 also turns on
and off the plurality of second solid-state light sources 23
together. The driver 21 can instantaneously perform the switching
of the state of the first solid-state light sources 22 and the
state of the second solid-state light sources 23 between on and off
in an electrical manner. The driver 21 is not necessarily provided
in the light source system 2 but may be provided in the controller
4.
[0069] The light modulator 3 modulates the light incident thereon
based on modulation signals D.sub.4 and D.sub.5 supplied from the
controller 4 and forms images. The light modulator 3 is formed of a
transmissive or reflective liquid crystal light valve, a digital
mirror device (DMD), or any other suitable spatial light modulator.
The light modulator 3 in the first embodiment is formed of a
transmissive liquid crystal light valve.
[0070] A parallelizing system, an illuminance homogenizing system,
and other optical components are provided as required in the
optical path between the light source system 2 and the light
modulator 3. The parallelizing system, which is formed of a field
lens or any other similar component, parallelizes the light to be
incident on the light modulator 3. The illuminance homogenizing
system, which is formed of a fly's-eye lens, a rod lens, or any
other similar component, homogenizes the illuminance distribution
of the light to be incident on the light modulator 3.
[0071] The controller 4 includes an interface 41, a timing
generating circuit 42, and an image processing circuit 43. The
interface 41 receives an electric signal D.sub.0 corresponding to
an input image from a signal source 9, such as a DVD player or a
computer, and separates the electric signal D.sub.0 into a sync
signal D.sub.1 and an image signal D.sub.2. The sync signal D.sub.1
contains data representing image display conditions, such as the
rate at which the input image is refreshed. The image signal
D.sub.2 contains grayscale data for each pixel. The thus separated
sync signal D.sub.i is outputted to the timing generating circuit
42. The thus separated image signal D.sub.2 is outputted to the
image processing circuit 43.
[0072] The ratio (hereinafter referred to as a duty) of the period
during which the first image B1 is displayed (hereinafter referred
to as a first display period) to the period during which the second
image B2 is displayed (hereinafter referred to as a second display
period) is set in advance at a variable or a fixed value. The duty
is set, for example, in accordance with the speed at which the
light modulator 3 responds. When the duty approaches 1, the speed
at which the light modulator 3 is required to respond decreases,
whereby the cost of the light modulator 3 can be reduced.
[0073] The duty is set also in accordance with, for example, the
visual angle sensitivity for the light L1 and L2 (optical
absorptance of the human pyramidal cells). To allow the viewer to
recognize the images B1 and B2 to be substantially the same in
brightness, the duty may be set in such a way that the optical
energy to be absorbed by the human pyramidal cells during the first
display period is equal to the optical energy to be absorbed by the
human pyramidal cells during the second display period based on the
difference in optical absorptance of the pyramidal cells between
the first and second wavelengths.
[0074] The timing generating circuit 42 generates a timing signal
D.sub.3 representing the first and second display periods based on
the thus set duty and the refresh rate of the input image. The
timing signal D.sub.3 is outputted to the driver 21 and the image
processing circuit 43.
[0075] In the example shown in FIG. 4, the duty is set at 1, and
the first display period and the second display period are set not
to overlap with each other. The length of the single-frame display
period is determined by the sync signal D.sub.1.
[0076] For example, when the refresh rate is 60 Hz and any single
frame does not include a period during which no image is displayed
(hereinafter referred to as a non-display period), the length of
the single-frame display period (t.sub.N to t.sub.N+1, N=0, 1, 2,
and so on) is 1/60 second. The length of the first display period
is 1/120 seconds, and the length of the second display period is
1/120 seconds.
[0077] The time at which the first display period starts (t.sub.0
in FIG. 4, for example) is shifted from the time at which the
second display period starts (t.sub.0.5 in FIG. 4, for example) by
approximately one-half the length of the single-frame display
period ( 1/120 second). The timing signal D.sub.3 contains data
representing the time at which the first display period starts and
the time at which the second display period starts.
[0078] The driver 21 keeps turning on the first solid-state light
sources 22 and turning off the second solid-state light sources 23
during the first display period determined by the timing signal
D.sub.3. The driver 21 keeps turning off the first solid-state
light sources 22 and turning on the second solid-state light
sources 23 during the second display period determined by the
timing signal D.sub.3.
[0079] The image processing circuit 43 not only performs a variety
of image processing operations, such as gamma correction, on the
image signal D.sub.2 but also processes the image signal D.sub.2 so
that the number of pixels of the image signal D.sub.2 matches that
of the light modulator 3. For example, when the number of pixels of
the image signal D.sub.2 is greater than that of the light
modulator 3, an image signal having pixels that matches that of the
light modulator 3 is generated by averaging data on grayscale of
each set of pixels contained in the image signal D.sub.2 into data
on grayscale of a single pixel.
[0080] The image processing circuit 43 generates a first modulation
signal D.sub.4 for the first image 31 and a second modulation
signal D.sub.5 for the second image B2 based on the image signal
D.sub.2. The image processing circuit 43 supplies the first
modulation signal D.sub.4 to the light modulator 3 in
synchronization with the timing at which the display of the first
image B1 starts, which is determined by the timing signal D.sub.3.
The image processing circuit 43 supplies the second modulation
signal D.sub.5 to the light modulator 3 in synchronization with the
timing at which the display of the second image B2 starts, which is
determined by the timing signal D.sub.3.
[0081] While the first solid-state light sources 22 are kept turned
on during the first display period, the light L1 is incident on the
light modulator 3 during the first display period. The light
modulator 3 receives the first modulation signal D.sub.4 during the
first display period and modulates the light L1 to form the first
image B1. Similarly, while the second solid-state light sources 23
are kept turned on during the second display period, the light L2
is incident on the light modulator 3 during the second display
period, and the light modulator 3 modulates the light L2 based on
the second modulation signal D.sub.5 to form the second image
B2.
[0082] FIG. 5 is a timing chart showing the operation timing
different from that in the example shown in FIG. 4. In the example
shown in FIG. 5, each single frame includes a non-display period.
In this case, the timing generating circuit 42 subtracts the length
of the non-display period in a single frame from the total length
of the single frame to determine the length of the display period
in the single frame and determines the lengths of the first and
second display periods based on the length of the display period in
the single frame and the duty. The timing generating circuit 42
generates the timing signal D.sub.3 by setting the non-display
period in such a way that the period between the first and second
display periods forms the non-display period and the non-display
period contains the time at which the operation of the light
modulator 3 is switched from the modulation for the first image to
the modulation for the second image (t.sub.0.5, for example). The
driver 21 keeps the first solid-state light sources 22 turned off
during the second display period and the non-display period and the
second solid-state light sources 23 turned off during the first
display period and the non-display period.
[0083] The speed at which the light modulator 3 responds is limited
depending on the type of light modulator (liquid crystal light
valve, for example). With a non-display period provided between the
first and second display periods, the solid-state light sources 22
and 23 are kept turned off during the transition period when the
modulation for the first image is switched to the modulation for
the second image. In this way, image quality will not be degraded
even when the light modulator 3 does not respond fast enough to the
switching between the light L1 and the light L2.
[0084] A description will be made of a method for generating the
modulation signals D.sub.4 and D.sub.5 with reference to FIGS. 6 to
8. FIGS. 6 and 7 describe a first method for generating the
modulation signals D.sub.4 and D.sub.5, and FIG. 8 describes a
second method for generating the modulation signals D.sub.4 and
D.sub.5. The first generation method is used in a case where the
number of pixels of an input image is greater than the number of
pixels of the light modulator 3. The second generation method is
used in a case where the number of pixels of the light modulator 3
is equal to the number of pixels of an input image.
[0085] In the description of the first generation method, it is
assumed that the number of pixels of the image signal D.sub.2 is
2048.times.1536 (QXGA) and the number of pixels of the light
modulator 3 is 1024.times.768 (XGA) for ease of description. As
shown in FIG. 6, let a(m, n) be the grayscale value of the pixel
having an address (m, n) and contained in the image signal D.sub.2,
where m is an integer greater than or equal to 0 but smaller than
or equal to 2047 and n is an integer greater than or equal to 0 but
smaller than or equal to 1535. Further, let b(i, j) be the
grayscale value of the pixel having an address (i, j) and contained
in the first modulation signal D.sub.4, and let c(i, j) be the
grayscale value of the pixel having the address (i, j) and
contained in the second modulation signal D.sub.5, where i is an
integer greater than or equal to 0 but smaller than or equal to
1023 and j is an integer greater than or equal to 0 but smaller
than or equal to 767.
[0086] Based on the grayscale values of the input image pixels
contained in each pixel P1, the image processing circuit 43
calculates the grayscale value of the pixel P1. In this
description, the range of the first image B1 coincides with the
range of the input image, and each pixel P1 contains a 2.times.2
array of pixels in the input image. As shown in FIG. 7, the image
processing circuit 43 averages grayscale values of four input image
pixels contained in the pixel of the first image B1 having an
address (i, j), which are a(2i, 2j), a(2i+1, 2j), a(2i, 2j+1), and
a(2i+1, 2j+1), and substitutes the average into b(i, j).
[0087] Similarly, based on the grayscale values of the input image
pixels contained in each pixel P2 of the second image B2, the image
processing circuit 43 calculates the grayscale value of the pixel
P2. The input image pixels contained in each pixel P2 are
determined by the amount of shift of the second image B2 relative
to the first image B1. The amount of shift is determined by the
positional relationship between the members in the optical path
adjustment system 5 (which will be described later).
[0088] Now, let .DELTA.W be the amount of shift, p be the size of
each of the pixels in the light modulator 3, N be an integer
including 0, and q be a decimal greater than 0 but smaller than 1.
.DELTA.W is expressed by the following equation (1):
.DELTA.W=p(N+q) (1)
[0089] In the equation (1), q represents the amount of shift of
each pixel P2 from the corresponding pixel P1. For example, when
the position of each pixel P2 is shifted from the position of the
corresponding pixel P1 by one-half the pixel size, q is equal to
0.5. When the amount of shift of the image B2 from the image B1 is
1.5 times the pixel size, N is equal to 1 and p is equal to 0.5,
and the amount of shift of each pixel P2 from the corresponding
pixel P1 is also one-half the pixel size.
[0090] As shown in FIG. 2B, when q is set in such a way that each
pixel P1 overlaps with a plurality of pixels P2, the gap between
the pixels P1 can be filled with the pixels P2 and the gap between
the pixels P2 can be filled with the pixels P1, whereby the
resolution can be effectively increased. In particular, when q is
set at a value greater than or equal to 0.25 but smaller than or
equal to 0.75, the degree of increase in resolution is high, and
when q is set at 0.5, the effective resolution is maximized. When
the pixels are arranged in a two-dimensional manner, shifting the
pixels in at least one of the arrangement directions allows the
resolution to be increased. Shifting the pixels in both the two
arrangement directions allows the resolution to be further
increased.
[0091] In the example shown in FIG. 6, the amount of pixel shift
.DELTA.Wi in the i direction (horizontal scan direction, for
example) is one-half the pixel size, and the amount of pixel shift
.DELTA.Wj in the j direction (vertical scan direction, for example)
is one-half the pixel size. As shown in FIG. 7, the image
processing circuit 43 averages grayscale values of four input image
pixels contained in the pixel of the second image B2 having the
address (i, j), which are a(2i+1, 2j+1), a(2i+2, 2j+1), a(2i+1,
2j+2), and a(2i+2, 2j+2), and substitutes the average into c(i,
j).
[0092] When the contour of a pixel P2 runs off the contour of the
corresponding pixels of the input image, the amount of pixel shift
can, for example, be one-quarter the pixel size. In this case, c(i,
j) may be determined, for example, by using an interpolation
process used to make the number of pixels of the input image equal
to the number of pixels of the light modulator. For example, c(i,
j) can be determined by performing weighting in proportional to the
reciprocal of the distance from the center of the pixel P2 to the
center of each of the input image pixels contained in the pixel
P2.
[0093] Pixels of the second image B2 can be located outside the
input image. In this case, the pixels of the second image B2 that
are located outside the input image may be displayed in black.
Further, each of c(1023, 0) to c(1023, 766) shown in FIG. 6, for
example, may have the average of the grayscale values of two input
image pixels contained in the corresponding pixel P2 or a black
grayscale value.
[0094] In the description of the second generation method, it is
assumed that the number of pixels of the image signal D.sub.2 is
1024.times.768 (XGA) and the number of pixels of the light
modulator 3 is 1024.times.768 (XGA) for ease of description. The
image processing circuit 43 substitutes a(i, j), which is the
grayscale value of the pixel of the input image having an address
(i, j), into b(i, j), which is the grayscale value of the pixel of
the first image B1 having the address (i, j). The image processing
circuit 43 averages grayscale values of four input image pixels
with which part of the pixel of the second image B2 having the
address (i, j) overlaps, which are a(i, j), a(i+1, j), a(i, j+1),
and a(i+1, j+1), and substitutes the average into c(i, j).
[0095] The optical path adjustment system 5 will now be described
with reference to FIGS. 9A, 9B, 9C, and 10.
[0096] FIG. 9A is a perspective view diagrammatically showing the
configuration of the optical path adjustment system 5. FIG. 9B is a
plan view projected onto the XZ plane and showing the optical path
A1 of the light L1 and the optical path A2 of the light L2 incident
on the optical path adjustment system 5. FIG. 9C is a plan view
projected onto the XY plane and showing the optical paths A1 and
A2. FIG. 10 shows graphs illustrating the reflection
characteristics of the wavelength selecting surface 51 versus the
spectrum of the light L1 and L2. In the XYZ orthogonal coordinate
system shown in FIGS. 9A to 9C, the X axis corresponds to the
optical paths A1 and A2 of the light L1 and the light L2 before
they are incident on the optical path adjustment system 5. The Y
axis corresponds, for example, to the i direction shown in FIG. 6
in the pixel arrangement of the light modulator 3, and the Z axis
corresponds, for example, to the j direction.
[0097] As shown in FIGS. 9A to 9C, the optical path adjustment
system 5 includes a wavelength selecting element 53 and a
reflection mirror 54. The wavelength selecting element 53 is
formed, for example, of a dichroic mirror and has the wavelength
selecting surface 51. The reflection mirror 54 is formed, for
example, of a dichroic mirror or a reflection mirror having a
reflection film formed thereon and has the reflection surface 52.
The reflection surface 52 is positioned to be substantially
parallel to the wavelength selecting surface 51. The reflection
mirror 54 in the present embodiment is an element formed separately
from the wavelength selecting element 53 and fixed thereto. The
direction V of a normal to the wavelength selecting surface 51 is
inclined to the X axis by .theta. [rad] when the normal is
projected on the XZ plane and inclined to the X axis by .phi. [rad]
when the normal is projected onto the XY plane.
[0098] As shown in FIG. 10, the wavelength selecting surface 51
transmits light having relatively short wavelengths in the visible
light range (hereinafter referred to as a transmission area) and
reflects light having relatively long wavelengths in the visible
light range (hereinafter referred to as a reflection area). The
reflectance of the wavelength selecting surface 51 is saturated to
the lowest value in the transmission area and saturated to the
highest value in the reflection area. In an intermediate area
between the transmission area and the reflection area, the
reflectance of the wavelength selecting surface 51 monotonously
increases as the wavelength of the incident light increases.
[0099] To separate the light L1 and L2 at the wavelength selecting
surface 51 with high precision, it is effective to narrow the width
of the intermediate area or narrow the spectral bandwidth of the
light L1 and L2. When the wavelength selecting surface 51 is formed
of a dichroic mirror, increasing the number of layers of a
multilayer film contained in the dichroic mirror narrows the width
of the intermediate area. Further, using LDs as the solid-state
light sources 22 and 23 narrows the spectral bandwidth of the light
L1 and L2.
[0100] The reflection surface may be formed, for example, of a
dichroic mirror, as in the case of the wavelength selecting surface
51. In this configuration, when part of the light L1 passes through
the wavelength selecting surface 51 and forms leakage light, part
of the leakage light passes through the reflection surface. The
leakage light having passed through the reflection surface is
removed from the optical path between the optical path adjustment
system and the projection system 6. As a result, an unwanted image
formed by the leakage light is less visible, which avoids decrease
in image quality due to the leakage light.
[0101] In the description, the average of the highest and lowest
reflectance values in the visible light range is referred to as an
intermediate value, and the wavelength at which the reflectance has
the intermediate value is referred to as a threshold value. When
the wavelength of the light incident on the wavelength selecting
surface 51 is greater than the threshold value, reflection of the
incident light off the wavelength selecting surface 51 dominates,
whereas when the wavelength of the incident light is smaller than
the threshold value, transmission of the incident light through the
wavelength selecting surface 51 dominates.
[0102] In the present embodiment, the first wavelength is set to be
greater than the threshold value, and the second wavelength is set
to be smaller than the threshold value. Setting the wavelength
bandwidth of the light L2 not to overlap with the wavelength
bandwidth of the light L1 allows the light L1 and the light L2 to
be separated at the wavelength selecting surface 51 with high
precision, which is advantageous in improving the image quality. It
is, however, noted that even when part of the wavelength bandwidth
of the light L2 overlaps with the wavelength bandwidth of the light
L1, the resolution of a displayed image can still be increased.
[0103] In FIG. 10, the light L1 and the light L2 have the same
maximum light intensity, but the light intensities of the light L1
and L2 may alternatively differ from each other. For example, when
the visual angle sensitivity described above for the first
wavelength differs from that for the second wavelength, the outputs
from the solid-state light sources 22 and 23 may be set to differ
from each other in such a way that the amounts of optical energy to
be absorbed by the human pyramidal cells during the first and
second display periods, provided that pixels having the same
grayscale are displayed, are substantially the same. In this way,
the viewer recognizes images B1 and B2 to be substantially the same
in brightness and hence the switching between the images B1 and B2
is unlikely visible, whereby the image quality can be improved.
[0104] The light L1 incident on the optical path adjustment system
5 is reflected on the wavelength selecting surface 51 and travels
toward the projection system 6. The light L2 incident on the
optical path adjustment system 5 passes through the wavelength
selecting surface 51, is incident on the reflection surface 52 and
reflected on the reflection surface 52, passes through the
wavelength selecting surface 51 again, and travels in substantially
the same direction as the light L1. To achieve the situation in
which the optical path A1 of the light L1 and the optical path A2
of the light L2 immediately before they are incident on the
projection system 6 are shifted from each other in a direction
substantially perpendicular to the optical axis of the projection
system 6, the optical paths of the light fluxes that exit out of
the optical path adjustment system 5 are adjusted in accordance
with the wavelength of the light fluxes.
[0105] As shown in FIG. 9B, after the light L2 exits out of the
optical path adjustment system 5, the optical path A2 of the light
L2 is shifted from the optical path A1 of the light L1 and
substantially in parallel thereto by .DELTA.X in the X direction.
As shown in FIG. 9C, after the light L2 exits out of the optical
path adjustment system 5, the optical path A2 of the light L2 is
shifted from the optical path A1 of the light L1 and substantially
in parallel thereto by .DELTA.Ya in the Y direction. .DELTA.X and
.DELTA.Ya are expressed by the following equations (2) and (3),
where d is the distance between the wavelength selecting surface 51
and the reflection surface 52. As seen from the equations (2) and
(3), .DELTA.X and .DELTA.Ya, which are the amounts of shift, are
determined by the distance (d) between the wavelength selecting
surface 51 and the reflection surface 52 and the angle of incidence
(.theta., .phi.) on the wavelength selecting surface 51.
.DELTA.X=2d.times.sin .theta. (2)
.DELTA.Ya=2d.times.sin .phi. (3)
[0106] According to the thus configured projector 1, the displayed
images B1 and B2 are temporally and spatially shifted from each
other, and the number of pixels of a single image into which the
images B1 and B2 are combined is greater than the number of pixels
of the light modulator 3. As a result, a high-resolution image can
be displayed without any increase in the number of pixels of the
light modulator 3, and an image display apparatus capable of
displaying a high-quality image can be provided at a low cost.
[0107] Further, the optical paths A1 and A2 of the light L1 and L2
having exited out of the optical path adjustment system 5 can be
shifted from each other without dynamic control of the optical path
adjustment system 5. Since it is not necessary to spatially move
the optical path adjustment system 5, the optical path adjustment
system 5 will not vibrate. As a result, the angles of incidence of
the light L1 and L2 on the optical path adjustment system 5 can be
controlled with high precision, whereby the amount of shift of the
image B2 from the image B1 will not vary. Since the optical path
adjustment system 5 will not vibrate, the components of the
apparatus will unlikely suffer from vibration-induced defects, and
no inconvenience, such as increase in frequency of maintenance of
the apparatus and decrease in lifetime of the apparatus, will
occur.
[0108] Since it is not necessary to electrically change the
refractive index or other characteristics of the optical path
adjustment system 5, no drive voltage is required for the optical
path adjustment system 5. Since the light source system 2 can be
driven by a typical drive voltage, the drive voltage required for
the entire apparatus will not increase.
[0109] Since the light source in the light source system 2 is
formed of the solid-state light sources 22 and 23, the state of the
light source can be instantaneously switched between on and off in
an electrical manner, whereby the first image B1 and the second
image B2 can be switched at precise timing. Therefore, a transition
period required for the switching between the images B1 and B2 can
be minimized, and the image quality will not be degraded because
the switching between the images will not be recognized.
[0110] The configuration described with reference to the first
embodiment is an example showing an aspect of the invention, and
the technical scope of the invention is not limited to the first
embodiment. A variety of changes can be made to the extent that
they do not depart from the substance of the invention. For
example, the first wavelength is longer than the second wavelength
in the first embodiment for ease of description, but the first
wavelength may alternatively be shorter than the second wavelength.
Variations of the light source system, the light modulator, and the
optical path adjustment system will be described below.
[0111] FIG. 11A is a schematic view showing the configuration of a
projector 1B of a first variation. The configuration of a light
source system 2B in the projector 1B differs from that in the first
embodiment. As shown in FIG. 11A, the light source system 2B
includes a first laser light source 22B, a second laser light
source 23B, a wavelength selecting element 24B, a light diffusing
element 25B, and a parallelizing element 26B.
[0112] The first laser light source 22B in the present variation
includes a first solid-state light source 221, a wavelength
conversion element 222, and a resonance mirror 223. The first
solid-state light source 221 emits light having a fundamental
wavelength (infrared light, for example). The wavelength conversion
element 222 is made, for example, of a lithium niobate crystal
having a periodically poled structure and converts at least part of
the incident light into light having a converted wavelength (green
light, for example). The resonance mirror 223 is characterized by
reflecting the light having the fundamental wavelength and
transmitting the light having the converted wavelength.
[0113] The light emitted from the first solid-state light source
221 travels back and forth multiple times between the first
solid-state light source 221 and the resonance mirror 223 for laser
oscillation. Part of the light emitted from the first solid-state
light source 221 is converted into the light having the converted
wavelength whenever passing through the wavelength conversion
element 222. The laser light whose wavelength has been converted by
the wavelength conversion element 222 passes through the resonance
mirror 223 and exits out of the laser light source 22B as light L1
having a first wavelength.
[0114] The second laser light source 23B, having the same
configuration as that of the first laser light source 22B, includes
a second solid-state light source 231, a wavelength conversion
element 232, and a resonance mirror 233. In the second laser light
source 23B, the wavelength of the light emitted from the second
solid-state light source 231 differs from the wavelength of the
light emitted from the first solid-state light source 221. The
wavelength conversion element 232 has conversion characteristics
corresponding to the wavelength of the light emitted from the
second solid-state light source 231. The resonance mirror 233 has
reflection/transmission characteristics corresponding to the
wavelength of the light emitted from the second solid-state light
source 231. The second laser light source 23B emits light L2 having
a second wavelength.
[0115] When the wavelengths directly produced in the laser devices
are used as the first and second wavelengths, the wavelength
conversion elements can be omitted. Alternatively, an intra-cavity
laser device may be used.
[0116] The wavelength selecting element 24B is characterized by
reflecting the light L1 having the first wavelength and
transmitting the light having the second wavelength. The wavelength
selecting element 24B is formed, for example, of a dichroic mirror
and in the present variation, has substantially the same
characteristics as those of the wavelength selecting element 53 in
the optical path adjustment system 5. The light L2 incident on the
wavelength selecting element 24B passes through the wavelength
selecting element 24B and impinges on the light diffusing element
25B. The light L1 incident on the wavelength selecting element 24B
is reflected on the wavelength selection element 24B, where the
traveling direction of the light L1 is deflected and substantially
coincides with the optical path of the light L2, and incident on
the light diffusing element 25B. Part of the light L1 that will
pass through the wavelength selection element 53 and form leakage
light passes through the wavelength selecting element 24B. In this
way, the leakage light is removed from the optical path between the
wavelength selecting element 24B and the light diffusing element
25B, whereby the amount of leakage light in the optical path
adjustment system 5 is reduced.
[0117] The light diffusing element 258 is formed, for example, of a
VHG or any other optical grating or a diffuser and diffuses the
light L1 and the light L2 before they exit therethrough. The light
diffusing element 25B, which is formed of a diffractive optical
element in the present variation, not only diffuses the light L1
and L2 but also changes the spot shapes of the light L1 and L2. The
light L1 and the light L2 having exited out of the light diffusing
element 25B are incident on the light modulator 3, where the spot
shapes of the light L1 and L2 are substantially similar to the area
where a plurality of pixels are arranged (rectangular area, for
example). The light L1 and L2 having exited out of the light
diffusing element 25B passes through the parallelizing element 26B
formed, for example, of a field lens, where the light L1 and L2 are
substantially parallelized, and impinges on the light modulator 3.
Thereafter, a first image B1 formed by the light L1 is displayed
and a second image B2 formed by the light L2 is displayed, as in
the first embodiment.
[0118] In the projector 1B, since each of the light L1 and the
light L2 is laser light, the spectral bandwidth thereof is
significantly narrower than that of the light emitted from an LED
or other similar light sources. It is therefore readily possible to
prevent the light intensity-versus-wavelength distribution of the
light L1 from overlapping with that of the light L2, whereby the
light L1 and the light L2 are readily separated at the wavelength
selecting surface 51.
[0119] Since part of the light that will form leakage light in the
optical path adjustment system 5 is removed by the wavelength
selecting element 24B, an unwanted image produced by the leakage
light is less visible. Even when the laser light sources 22B and
23B are replaced with LEDs or other similar light sources, the
advantageous effect of making an unwanted image produced by leakage
light less visible can be provided. A light source system formed of
both an LED and an LD may alternatively be used. For example, the
first solid-state light source may be formed of an LED, and the
second solid-state light source may be formed of an LD.
[0120] FIG. 11B is a schematic view showing the configuration of a
projector 1C of a second variation. As shown in FIG. 11B, the
projector 1C includes a light source system 2C, a light modulator
3C, a controller 4C, the optical path adjustment system 5, and the
projection system 6.
[0121] The light source system 2C includes a lamp light source 21C,
a color wheel 22C, and an illuminance homogenizing element 23C. The
lamp light source 21C emits light L0 having first and second
wavelengths. The color wheel 22C is, for example, a plate having a
substantially circular shape and installed in a rotatable manner.
The color wheel 22C includes first and second color filters. The
first color filter transmits light having the first wavelength and
absorbs light having the second wavelength. The second color filter
absorbs light having the first wavelength and transmits light
having the second wavelength. As the color wheel 22C rotates, light
L1 having the first wavelength and light L2 having the second
wavelength are switched with time to exit through the color wheel
22C.
[0122] The light L1 and the light L2 having exited through the
color wheel 22C are incident on the illuminance homogenizing
element 23C, where the illuminance thereof is homogenized, and then
incident on the light modulator 3C. The light modulator 3C is
formed of a digital mirror device having a mirror provided for each
pixel. The controller 4C monitors the rotation of the color wheel
22C and outputs first and second modulation signals to the light
modulator 3C switched with time in synchronization with the
rotation of the color wheel 22C. The light modulator 3C controls
the orientation of the mirror for each pixel in accordance with the
first and second modulation signals to control the direction in
which the incident light is reflected for each pixel. The light L1
and the light L2 having exited out of the light modulator 3C travel
via the optical path adjustment system 5 and the projection system
6 and are displayed as first and second images on a projection
surface, as in the first embodiment.
[0123] In the projector 1C, since the wavelength of the light
emitted from the light source system 2C is temporally switched, the
configuration of the light source system 2C can be simplified. The
color wheel 22C may vibrate when rotated, but the effect of the
vibration of the color wheel 22C on the optical paths of the light
L1 and L2 is significantly smaller than the effect in a case where
the optical path adjustment system 5 vibrates. Therefore, the
amount of shift by which optical paths are shifted from each other
can be set more precisely than in a configuration in which the
optical path adjustment system itself is spatially moved, and
decrease in image quality due to vibration will not occur.
[0124] FIG. 12A is a side view showing the configuration of an
optical path adjustment system 5D of a third variation. The optical
path adjustment system 5D differs from the optical path adjustment
system 5 shown in FIG. 9C in that a guide 55D formed, for example,
of a reflection mirror is provided. The guide 55D reflects the
light L1 and the light L2 having traveled via the wavelength
selecting surface 51 toward the projection system 6.
[0125] The angle between the direction in which the light L1 and L2
travels and a projector body changes after the light L1 and the
light L2 are incident on the wavelength selecting surface 51 or the
reflection surface and travel therethrough. The position and the
attitude of the guide 55D is set in such a way that the angle
between the direction in which the light L1 and L2 travels and the
projector body does not change before and after the incidence of
the light L1 and L2 on the optical path adjustment system 5D.
[0126] In the present variation, the position and the attitude of
the guide 55D is set in such a way that the direction in which the
light L1 and L2 having exited out of the optical path adjustment
system 5D travels is substantially parallel to the optical axis 6A
of the projection system 6. In this way, the angle between the
direction in which the light L1 and L2 travels and the horizontal
plane or any other plane does not change before and after the
incidence of the light L1 and L2 on the optical path adjustment
system 5D, whereby the descending vertical angle or the ascending
vertical angle of the light L1 and L2 that exits out of the
projector can be readily controlled.
[0127] FIG. 12B is a schematic view showing the configuration of an
optical path adjustment system 5E of a fourth variation. The
optical path adjustment system 5E includes a substrate 50E, and a
reflection film 51E and a dielectric multilayer film 52E stacked on
the substrate 50E. The dielectric multilayer film 52E has a
structure in which two types of layer having different refractive
indices are alternately stacked. The refractive index and the
thickness of each of the layers that form the dielectric multilayer
film 52E are adjusted in such a way that the dielectric multilayer
film 52E reflects light L1 having a first wavelength and transmits
light L2 having a second wavelength. The front surface of the
reflection film 51E functions as a reflection surface, and the
front surface of the dielectric multilayer film 52E functions as a
wavelength selecting surface. In the thus configured optical path
adjustment system 5E, the reflection surface is formed on the same
optical element on which the wavelength selecting surface is
formed.
[0128] In the optical path adjustment system 5E, the distance
between the reflection surface and the wavelength selecting surface
is determined by the thickness of the dielectric multilayer film
52E. The distance between the reflection surface and the wavelength
selecting surface can therefore be controlled with high precision.
The distance can, for example, be controlled with pixel-size
precision (with micrometer precision, for example). Further, since
the reflection surface is formed on the same optical element on
which the wavelength selecting surface is formed, the distance
between the reflection surface and the wavelength selecting surface
unlikely changes over time, and hence the amount of shift of the
optical path of the light L2 from the optical path of the light L1
unlikely changes over time.
[0129] Alternatively, the reflection surface and the wavelength
selecting surface may be formed on the same optical element by
forming the reflection surface on one side of a transparent glass
substrate or any other suitable substrate and forming the
wavelength selecting surface on the other side. In this case, the
distance between the reflection surface and the wavelength
selecting surface can readily be increased, as compared with the
case where the distance between the reflection surface and the
wavelength selecting surface is set depending only on the thickness
of the dielectric multilayer film.
[0130] FIG. 12C is a schematic view showing the configuration of an
optical path adjustment system 5F of a fifth variation. The optical
path adjustment system 5F includes wavelength selecting elements
51F and 52F and reflection mirrors 53F and 54F. Each of the
wavelength selecting elements 51F and 52F has the same
characteristics as those of the wavelength selecting element 53 in
the first embodiment. The reflection mirrors 53F and 54F are
characterized by reflecting light having a first wavelength. The
wavelength selecting element 51F and 52F and the reflection mirrors
53F and 54F form a mirror system.
[0131] The wavelength selecting element 51F is disposed in such a
way that the angle of incidence of image light on the wavelength
selecting element 51F is approximately degrees and inclined to the
wavelength selecting element 52F by approximately 90 degrees. The
wavelength selecting element 51F is disposed substantially in
parallel to the reflection mirror 53F. The wavelength selecting
element 52F is disposed substantially in parallel to the reflection
mirror 54F. The distance between the wavelength selecting element
51F and the reflection mirror 53F differs from the distance between
the wavelength selecting element 52F and the reflection mirror
54F.
[0132] In the optical path adjustment system 5F, the light L1 and
the light L2 are first incident on the wavelength selecting element
51F. The light L2 passes through the wavelength selecting element
51F, impinges on the wavelength selecting element 52F, passes
through the wavelength selecting element 52F, and exits out of the
optical path adjustment system 5F.
[0133] The light L1 is reflected on the wavelength selecting
element 51F, sequentially reflected on the reflection mirrors 53F
and 54F, and incident on the wavelength selecting element 52F. The
light L1 incident on the wavelength selecting element 52F is
reflected on the wavelength selecting element 52F and exits out of
the optical path adjustment system 5F along with the light L2
having passed through the wavelength selecting element 52F. The
traveling direction of the light L1 is deflected each time the
light L1 is reflected, and the optical path of the light L1 at the
time when the light L1 exits out of the optical path adjustment
system 5F becomes substantially parallel to the optical path of the
light L2 but is spaced apart therefrom by the amount of shift.
[0134] As described above, adjusting the optical path of the light
L1 reflected on the wavelength selecting surface also allows the
optical path of the light L1 reflected on the wavelength selecting
surface to be shifted from the optical path of the light L2 having
passed through the wavelength selecting surface. The mirror system
can alternatively be formed of a plurality of reflection members.
Each of the reflection mirrors 53F and 54F may be formed of a
dichroic mirror, which may, for example, have substantially the
same characteristics as those of the wavelength selecting elements
51F and 52F.
[0135] FIG. 13 is a perspective view showing the configuration of
an optical path adjustment system 5G of a sixth variation. The
optical path adjustment system 5G includes wavelength selecting
elements 51G and 53G and reflection mirrors 52G and 54G, which are
similar to those in the first embodiment. The wavelength selecting
element 51G is paired with the reflection mirror 52G, and the
wavelength selecting element 53G is paired with the reflection
mirror 54G.
[0136] The wavelength selecting surface of the wavelength selecting
element 51G is substantially parallel to the reflection surface of
the reflection mirror 52G. The wavelength selecting surface and the
reflection surface are substantially parallel to a plane obtained
by rotating the XZ plane (or the YZ plane) around the Z axis by
approximately 45 degrees.
[0137] The wavelength selecting surface of the wavelength selecting
element 53G is substantially parallel to the reflection surface of
the reflection mirror 54G. The wavelength selecting surface and the
reflection surface are substantially parallel to a plane obtained
by rotating the XZ plane (or the XY plane) around the X axis by
approximately 45 degrees.
[0138] The light L1 and the light L2 having exited out of the light
modulator 3 travel in the positive X direction and impinges on the
wavelength selecting element 51G. The light L1 is reflected on the
wavelength selecting element 51G, where the traveling direction of
the light L1 is deflected by approximately 90 degrees, and travels
in the negative Y direction. The light L2 passes through the
wavelength selecting element 51G, is then reflected on the
reflection mirror 52G, where the traveling direction of the light
L2 is deflected by approximately 90 degrees, passes through the
wavelength selecting element 51G again, and travels in the negative
Y direction. The optical path of the light L1 reflected on the
wavelength selecting element 51G is shifted from the optical path
of the light L2 reflected on the reflection mirror 52G by .DELTA.X
in the X direction.
[0139] The light L1 and the light L2 traveling via the wavelength
selecting element 51G in the negative Y direction are incident on
the wavelength selecting element 53G. The light L1 is reflected on
the wavelength selecting element 53G, where the traveling direction
of the light L1 is deflected by approximately 90 degrees, and
travels in the positive Z direction. The light L2 passes through
the wavelength selecting element 53G, is then reflected on the
reflection mirror 54G, where the traveling direction of the light
L2 is deflected by approximately 90 degrees, passes through the
wavelength selecting element 53G again, and travels in the positive
Z direction. The optical path of the light L1 reflected on the
wavelength selecting element 53G is shifted from the optical path
of the light L2 reflected on the reflection mirror 54G by .DELTA.Y
in the Y direction.
[0140] The light L1 and the light L2 having traveled via the
wavelength selecting element 53G are incident on the projection
system 6. The optical path of the light L1 is shifted from the
optical path of the light L2 by .DELTA.X in the X direction and
.DELTA.Y in the Y direction when they are incident on the
projection system 6.
[0141] As described with reference to the thus configured optical
path adjustment system 5G, a set of a wavelength selecting surface
and a reflection surface may be provided for each direction where
the optical paths of the light L1 and L2 are shifted from each
other. In this way, .DELTA.X can be set in accordance with the
distance between the wavelength selecting element 51G and the
reflection mirror 52G, and .DELTA.Y can be set in accordance with
the distance between the wavelength selecting element 53G and the
reflection mirror 54G. That is, the amounts of shift in the two
directions can be set independently.
Second Embodiment
[0142] A projector of a second embodiment will next be described
with reference to FIGS. 14, 15, 16A, and 16B. FIGS. 14 and 15 are
schematic views showing the configuration of a projector 7 of the
second embodiment. FIG. 16A is a timing chart showing image display
timing for each hue. FIG. 16B is a conceptual diagram of an entire
displayed image. FIG. 14 shows a state in which a first image B3 is
displayed, and FIG. 15 shows a state in which a second image B4 is
displayed.
[0143] The projector 7 includes three image formation systems 70r,
70g, and 70b, a controller 71, a light combining element 76, and a
projection system 77. The configuration of each of the image
formation systems 70r, 70g, and 70b is the same as the
configuration of the projector 1 of the first embodiment from which
the projection system 6 is removed. In the second embodiment, the
image formation system 70g is disposed along a first optical path
7A of the light that exits out of the light combining element 76
but on the side opposite to the projection system 77. The image
formation systems 70r and 70b are disposed on opposite sides of the
light combining element 76 and face each other in a direction
substantially perpendicular to the first optical path 7A.
[0144] The controller 71 supplies a timing signal D.sub.3 to each
of the image formation systems 70r, 70g, and 70b. During a first
display period, the controller 71 supplies a modulation signal
Dr.sub.4 for first red light Lr1 to the image formation system 70r,
a modulation signal Dg.sub.4 for first green light Lg1 to the image
formation system 70g, and a modulation signal Db.sub.4 for first
blue light Lb1 to the image formation system 70b. During a second
display period, the controller 71 supplies a modulation signal
Dr.sub.5 for second red light Lr2 to the image formation system
70r, a modulation signal Dg.sub.5 for second green light Lg2 to the
image formation system 70g, and a modulation signal Db.sub.5 for
second blue light Lb2 to the image formation system 70b.
[0145] As shown in FIGS. 16A and 16B, during the first display
period, a first red image, a first green image, and a first blue
image are displayed in substantially the same position so that a
full-color first image B3 is displayed. During the second display
period, a second red image, a second green image, and a second blue
image are displayed in substantially the same position so that a
full-color second image B4 is displayed. The position of each pixel
that forms the second image B4 is shifted from the position of each
pixel that forms the first image B3.
[0146] The image formation system 70r includes the controller 71, a
light source 72r, a field lens 73r, light modulator 74r, and an
optical path adjustment system 75r. The light source 72r and the
field lens 73r form a light source system. The light source 72r
emits the first red light Lr1 and the second red light Lr2 based on
the timing signal D.sub.3 switched with time. Each of the first red
light Lr1 and the second red light Lr2 has a spectral peak in a
wavelength band that belongs to a red hue (wavelength longer than
or equal to 625 nm but shorter than or equal to 740 nm, for
example).
[0147] The red light Lr1 and the red light Lr2 emitted from the
light source 72r are incident on the field lens 73r, where they are
parallelized, and then incident on the light modulator 74r. The red
light Lr1 and the red light Lr2 incident on the light modulator 74r
undergo time division modulation and then impinge on the optical
path adjustment system 75r. The red light Lr1 incident on the
optical path adjustment system 75r is reflected on a wavelength
selecting element 751r and incident on the light combining element
76. The red light Lr2 incident on the optical path adjustment
system 75r passes through the wavelength selecting element 751r, is
then reflected on a reflection mirror 752r, passes through the
wavelength selecting element 751r again, and impinges on the light
combining element 76.
[0148] The image formation system 70g has the same configuration as
that of, the image formation system 70r. A light source 72g emits
the first green light Lg1 and the second green light Lg2 switched
with time. Each of the first green light Lg1 and the second green
light Lg2 has a spectral peak in a wavelength band that belongs to
a green hue (wavelength longer than or equal to 500 nm but shorter
than or equal to 565 nm, for example).
[0149] The green light Lg1 and the green light Lg2 are incident on
a field lens 73g, where they are parallelized, and incident on a
light modulator 74g, where they undergo time division modulation.
The green light Lg1 incident on an optical path adjustment system
75g is reflected on a wavelength selecting element 751g and
incident on the light combining element 76. The green light Lg2
incident on the optical path adjustment system 75g passes through
the wavelength selecting element 751g, is reflected on a reflection
mirror 752g, then passes through the wavelength selecting element
751g again, and impinges on the light combining element 76.
[0150] The image formation system 70b differs from the image
formation systems 70r and 70g in that a wavelength selecting
element 751b transmits the first blue light Lb1 and reflects the
second blue light Lb2. A light source 72b emits the first blue
light Lb1 and the second blue light Lb2 switched with time. Each of
the first blue light Lb1 and the second blue light Lb2 has a
spectral peak in a wavelength band that belongs to a blue hue
(wavelength longer than or equal to 450 nm but shorter than or
equal to 485 nm, for example).
[0151] The blue light Lb1 and the blue light Lb2 are incident on a
field lens 73b, where they are parallelized, and incident on a
light modulator 74b, where they undergo time division modulation.
The blue light Lb1 incident on an optical path adjustment system
75b passes through a wavelength selecting element 751b, is
reflected on a reflection mirror 752b, then passes through the
wavelength selecting element 751b again, and impinges on the light
combining element 76. The blue light Lb2 incident on the optical
path adjustment system 75b is reflected on the wavelength selecting
element 751b and incident on the light combining element 76.
[0152] The light combining element 76 is formed of a dichroic
prism. The dichroic prism has two types of wavelength selective
reflection film provided therein. One of the two types of
reflection film is characterized by reflecting the red light Lr1
and Lr2 and transmitting the green light Lg1 and Lg2 and the blue
light Lb1 and Lb2. The other one of the two types of reflection
film is characterized by reflecting the blue light Lb1 and Lb2 and
transmitting the green light Lg1 and Lg2 and the red light Lr1 and
Lr2. The two types of reflection film are disposed to be
perpendicular to each other. In the second embodiment, one of the
reflection films is inclined to the optical paths of the red light
Lr1 and Lr2 that have not yet been incident on the light combining
element 76 by approximately 45 degrees. The other one of the
reflection films is inclined to the optical paths of the blue light
Lb1 and Lb2 that have not yet been incident on the light combining
element 76 by approximately 45 degrees.
[0153] During the first display period, the optical path of the
first red light Lr1 to be incident on the light combining element
76 through the image formation system 70r substantially coincides
with the optical path of the first blue light Lg1 to be incident on
the light combining element 76 through the image formation system
70b. The traveling directions of the red light Lr1 and the blue
light Lb1 that are incident on the light combining element 76 and
exit out thereof are deflected and substantially coincide with the
optical path of the green light Lg1 (first optical path 7A) having
passed through the light combining element 76. That is, the first
red light Lr1, the first green light Lg1, and the first blue light
Lb1 incident on the light combining element 76 are combined with
their optical paths aligned with the first optical path 7A and then
projected on a projection surface S through the projection system
77.
[0154] During the second display period, the optical path of the
second red light Lr2 to be incident on the light combining element
76 through the image formation system 70r is shifted from the
optical path of the second blue light Lb2 to be incident on the
light combining element 76 through the image formation system 70b.
The traveling directions of the red light Lr2 and the blue light
Lb2 that are incident on the light combining element 76 and exit
out thereof during the second display period are deflected and
substantially coincide with the optical path of the green light Lg2
having passed through the light combining element 76. That is, the
second red light Lr2, the second green light Lg2, and the second
blue light Lb2 incident on the light combining element 76 are
combined with their optical paths aligned with a second optical
path 7B and then projected on the projection surface S through the
projection system 77.
[0155] A description will be made of the direction in which the
light exiting position is shifted when the light incident position
on the light combining element 76 is shifted. Consider the
following configuration (referred to as Comparative Example) and
compare it with the present embodiment: In Comparative Example, the
positive or negative directions in which the red and blue light
incident positions on the light combining element are shifted (the
direction along the first optical path 7A) during the first display
period is the same as those during the second display period.
Comparative Example has, for example, a configuration in which the
first blue light is reflected on a wavelength selecting element
during the first display period and the second blue light passes
through the wavelength selecting element during the second display
period.
[0156] In the configuration of Comparative Example, when the first
display period transits to the second display period, the optical
path of the blue light having exited out of the light combining
element 76 is shifted toward the red light image formation system
and the optical path of the red light having exited out of the
light combining element 76 is shifted toward the blue light image
formation system. That is, the positions where the blue light and
the red light exit out of the light combining element 76 are
shifted in opposite directions.
[0157] In the present embodiment, the directions in which the
positions where the light fluxes from the image formation systems
70r and 70b are incident on the light combining element 76 are
shifted during the first display period are opposite to those
during the second display period. As a result, the directions in
which the positions where the light fluxes from the image formation
systems 70r and 70b exit out of the light combining element 76 are
shifted during the first display period are the same as those
during the second display period, whereby the optical paths of the
light fluxes having traveled via the light combining element 76 can
be aligned with each other during both the first and second display
periods.
[0158] Since the second optical path 7B corresponding to the second
image B4 is shifted from the first optical path 7A corresponding to
the first image B3, the second image B4 is displayed in a position
shifted from the position where the first image B3 is displayed, as
shown in FIG. 16B. The displayed images B3 and B4 are switched with
time fast enough not to allow the viewer to be aware of the
switching. The viewer observes the images B3 and B4 superimposed
with the positions of the pixels thereof shifted from each other,
whereby an effectively high-resolution image is displayed.
[0159] As described above, the projector 7, which can display an
image having a large number of hues, is capable of displaying a
high-quality image.
[0160] As a configuration in which the directions in which the
optical paths are shifted from each other by the image formation
systems disposed on opposite sides of the light combining element
during the first display period are opposite to those during the
second display period, the following configurations can also be
employed: In a first exemplary configuration, first blue light Lb1
is reflected on a wavelength selecting element; second blue light
Lb2 passes through the wavelength selecting element; first red
light Lr1 passes through another wavelength selecting element; and
second red light Lr2 is reflected on the other wavelength selecting
element. To achieve the configuration, the configurations of the
light sources or the characteristics of the wavelength selecting
elements may be changed.
[0161] In a second exemplary configuration, the direction in which
the light emitted from a light source system and directed toward an
optical path adjustment system travel in an image formation system
disposed on one side of a light combining element is opposite to
that in another image formation system disposed on the other side
of the light combining element. To achieve the configuration, for
example, the position of the image formation system corresponding
to the blue light may be reversed with respect to a plane
perpendicular to the first optical path 7A. The fact that the blue
light image is reversed can be compensated by adjusting the
arrangement of the pixels in a modulation signal.
[0162] Alternatively, the direction in which the optical paths of
the blue light are shifted from each other may differ from the
direction in which the optical paths of the red light are shifted
from each other. In either case, a modulation signal representing
data that the pixels should display in shifted positions may be
produced based, for example, on data on input image pixels
corresponding to the positions of the displayed pixels.
Third Embodiment
[0163] A projector of a third embodiment will next be described
with reference to FIGS. 17, 18, 19, 20A, and 20B. FIGS. 17 and 18
are schematic views showing the configuration of a projector 8 of
the third embodiment. FIG. 19 shows graphs illustrating the
characteristics of a wavelength selecting surface versus first to
fourth wavelengths. FIG. 20A is a timing chart showing image
display timing for each hue, and FIG. 208 is a conceptual diagram
of an entire displayed image. FIG. 17 shows a state in which a
first image B5 is displayed, and FIG. 18 shows a state in which a
second image 86 is displayed.
[0164] The third embodiment is similar to the second embodiment in
that an image is displayed by using a plurality of color light
fluxes having different wavelengths. The third embodiment differs
from the second embodiment in that the optical paths of one of the
plurality of color light fluxes are shifted from each other when
the first display period transits to the second display period.
[0165] As shown in FIGS. 17 and 18, the projector 8 includes three
image formation systems 80r, 80g, and 80b, a controller 81, a light
combining element 85, an optical path adjustment system 86, and a
projection system 87. The image formation system 80g is disposed
along a first optical path 8A of the light that exits out of the
light combining element 85 but on the side opposite to the optical
path adjustment system 86. The image formation systems 80r and 80b
are disposed on opposite sides of the light combining element 85
and face each other in a direction substantially perpendicular to a
first optical path 8A.
[0166] The controller 81 supplies a modulation signal Dr for red
light to the image formation system 80r and a modulation signal Db
for blue light to the image formation system 80b throughout the
first and second display periods. The controller 81 supplies a
modulation signal Dg.sub.4 for first green light Lg1 to the image
formation system 80g during the first display period. The
controller 81 supplies a modulation signal Dg.sub.5 for second
green light Lg2 to the image formation system 80g during the second
display period.
[0167] As shown in FIGS. 20A and 20B, during the first display
period, a red image, a first green image, and a blue image are
displayed in substantially the same position so that a full-color
first image B5 is displayed. The red image and the blue image are
kept displayed during the second display period following the first
display period. During the second display period, a second green
image is displayed instead of the first green image. The position
of each pixel of the second green image is shifted from the
position of each pixel of the first green image. During the second
display period, the red image, the second green image, and the blue
image form a full-color second image B6.
[0168] The image formation system 80g includes a light source 82g,
a field lens 83g, and a light modulator 84g. The light source 82g
and the field lens 83g form a light source system. The light source
82g emits the green light Lg1 having a first wavelength and the
green light Lg2 having a second wavelength based on a timing signal
D.sub.3 switched with time. The green light Lg1 and the green light
Lg2 emitted from the light source 82g are incident on the field
lens 83g, where they are parallelized, and then incident on the
light modulator 84g. The light modulator 84g modulates the first
green light Lg1 based on the modulation signal Dg.sub.4 and
modulates the second green light Lg2 based on the modulation signal
Dg.sub.5. The light Lg1 and the light Lg2 modulated by the light
modulator 84g impinge on the light combining element 85, pass
through the light combining element 85, and impinge on the optical
path adjustment system 86. The optical paths of the green light Lg1
and Lg2 having exited out of the light combining element 85
substantially coincide with the first optical path 8A.
[0169] The image formation system 80r includes a light source 82r,
a field lens 83r, and a second light modulator 84r. The light
source 82r and the field lens 83r form a second light source
system. The light source 82r emits red light Lr having a third
wavelength longer than the first and second wavelengths. The red
light Lr emitted from the light source 82r is incident on the field
lens 83r, where they are parallelized, and then incident on the
second light modulator 84r. The second light modulator 84r
modulates the red light Lr based on the modulation signal Dr. The
red light Lr modulated by the second light modulator 84r impinges
on the light combining element 85, where the traveling direction of
the red light Lr is deflected, and exits out of the light combining
element 85 along the first optical path 8A. The red light Lr having
exited out of the light combining element 85 impinges on the
optical path adjustment system 86.
[0170] The image formation system 80b includes a light source 82b,
a field lens 83b, and a third light modulator 84b. The light source
82b and the field lens 83b form a third light source system. The
light source 82b emits blue light Lb having a fourth wavelength
shorter than the first and second wavelengths. The blue light Lb
emitted from the light source 82b is incident on the field lens
83b, where they are parallelized, and then incident on the third
light modulator 84b. The third light modulator 84b modulates the
blue light Lb based on the modulation signal Db. The blue light Lb
modulated by the third light modulator 84b impinges on the light
combining element 85, where the traveling direction of the blue
light Lb is deflected, and exits out of the light combining element
85 along a second optical path 8B. The blue light Lb having exited
out of the light combining element 85 impinges on the optical path
adjustment system 86.
[0171] During the first display period, the first green light Lg1
incident on the optical path adjustment system 86 is reflected on a
wavelength selecting element 861 and travels along a third optical
path 8C. The first green light Lg1 having exited out of the optical
path adjustment system 86 enters the projection system 87 and is
projected on a projection surface S.
[0172] During the second display period, the second green light Lg2
incident on the optical path adjustment system 86 passes through
the wavelength selecting element 861, is reflected on a reflection
mirror 862, and travels along a fourth optical path 8D. The second
green light Lg2 reflected on the reflection mirror 862 passes the
wavelength selecting element 861 again, enters the projection
system 87, and is projected on the projection surface S.
[0173] As described above, since the optical paths of the green
light Lg1 and Lg2 are shifted from each other in the optical path
adjustment system 86, the second green image is displayed in a
position different from the position where the first green image is
displayed.
[0174] Throughout the first and second display periods, the red
light Lr incident on the optical path adjustment system 86 is
reflected on the wavelength selecting element 861 and travels along
the third optical path 8C. The red light Lr having exited out of
the optical path adjustment system 86 enters the projection system
87 and is projected on the projection surface S.
[0175] Throughout the first and second display periods, the blue
light Lb incident on the optical path adjustment system 86 passes
through the wavelength selecting element 861, is reflected on the
reflection mirror 862, and travels along the third optical path 8C.
The blue light Lb reflected on the reflection mirror 862 passes
through the wavelength selecting element 861 again, enters on the
projection system 87, and is projected on the projection surface
S.
[0176] Looking at the relationship between the optical path of the
blue light Lb and the optical path of the red light Lr, one can see
that the optical path of the blue light Lb is shifted from the
optical path of the red light Lr substantially in parallel thereto
after the blue light Lb and the red light Lr travel via the optical
path adjustment system 86. To cancel the optical path shift in the
optical path adjustment system 86, the second optical path 8B is
set to be shifted from the first optical path 8A. Specifically, the
arrangement of the image formation systems 80b and 80r is adjusted
in such a way that the position where the light from the image
formation system 80b is incident on the light combining element 85
is shifted from the position where the light from the image
formation system 80r is incident on the light combining element 85.
In this way, the red image and the blue image are displayed in
substantially the same position as the position where the first
green image is displayed throughout the first and second display
periods.
[0177] The thus configured projector 8, which can display an image
having a large number of hues, is capable of displaying a
high-quality image. As compared with the projector of the second
embodiment, the number of optical path adjustment systems can be
reduced, whereby the configuration of the apparatus can be
simplified. Since the pixels of an image of a color for which the
visual angle sensitivity is relatively high among a plurality of
colors (red, green, and blue) are shifted, a sense of high
resolution is provided in an effective manner. The projector 8
having a simple configuration described above can still display a
high-quality image.
[0178] In the projectors of the second and third embodiments, the
light source systems, the light modulators, and the optical path
adjustment systems can be changed as appropriate by employing the
variety of variations described above. For example, the light
source system in the image formation system 80g may be the light
source system 2C shown in FIG. 11B.
[0179] The entire disclosure of Japanese Patent Application No.
2009-242512, filed Oct. 21, 2009 is expressly incorporated by
reference herein.
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